Breast cancer cells have been shown to promote bone resorption by enhancing osteoclast formation and function via a number of factors derived from the tumor including M-CSF, transforming growth factor (TGF)-β, tumor necrosis factor α, insulin-like growth factor II, parathyroid hormone related peptide, IL-1, IL-6 and IL-11[2,5-7]. The gene discussed is CSF1; the disease is breast carcinoma.